Daytronic Corporation-AC Strain Gage Instrument (Model 4078)

Being a phase-sensitive carrier-demodulator instrument (rather than fully DC), the single-channel Model 4078 is intended for applications involving transformer coupling to the transducer bridge (as with rotary-transformer torque sensors) and for applications requiring high sensitivity with optimum signal-to-noise characteristics—as, for example, where the electrical environment is especially noisy and there is a need for high amplification of low signal levels.

Responding only to the modulated carrier frequency, the 4078 rejects extraneous voltages that can cause errors in DC systems.  Excitation is fixed at 3 VAC (rms) at 3280 Hz.

Other important 4078 features include

• Remote sensing and regulation of bridge excitation—eliminates errors from temperature effects on cable resistance and yields consistently stable ratiometric measurement, unaffected by possible power-supply drift
• High input impedance preserves the validity of factory calibration, prevents conversion of common-mode to normal-mode signals, and eliminates remaining errors attributable to cable resistance.  Allowable cable length has virtually no practical limits.
• User-adjustable phase and symmetry controls for accurate calibration